Two types of C3 nephritic factor: properdin-dependent C3NeF and properdin-independent C3NeF

The IgG fraction of serum from patients with membranoproliferative glomerulonephritis (MPGN) types I and II or partial lipodystrophy (PLD) was found to contain C3 nephritic factor (C3NeF) which reacts with the alternative pathway C3 convertase C3bBb and stabilizes it. Two types of C3NeF were detected, of which one was heat sensitive (56 degrees C for 30 min) and properdin dependent (C3NeF:P) but the other was heat stable and properdin independent (C3NeF:nP). C3NeF:P was found in sera from patients with MPGN types I and II and it displayed the properties of properdin and IgG. C3NeF:P was observed in patients with reduced serum concentrations of C3 and terminal complement components (TCC), and the generation of SC5b-9 complex was increased in mixtures with normal human serum. C3NeF:nP was found in sera from patients with MPGN type II and PLD, whose sera revealed a selective decrease in C3 concentrations.